Oscillator circuit having means to cyclically produce high frequency pulses



29, 1961 w. MOORE, JR 2,998,574

HAVING MEANS TO CYCLICALLY OSCILLATOR CIRCUIT PRODUCE HIGH FREQUENCYPULSES Original Filed Nov. 28, 1.952

li"t0UOOOIOOII OOOOOOOIOOQOICI INVENTOR. WARREN MOORE JR.

ATTORNEY.

United States Patent 2,998,574 OSCILLATOR CIRCUIT HAVING MEANS T0CYCLICALLY PRODUCE HIGH FREQUENCY PULSES Warren Moore, Jr., North Hills,Pa., assignor to Minneapolis-Honeywell Regulator Company, Minneapolis,Minn., a corporation of Delaware Original application Nov. 28, 1952,Ser. No. 323,069, new Patent No. 2,868,458, dated Jan. 13, 1959. Dividedand this application Apr. 17, 1958, Ser. No. 729,160

2 Claims. (Cl. 331-65) This application is a division of my copendingapplication Serial No. 323,069, filed November 28, 1952, Patent No.2,868,458, issued Jan. 13, 1959, entitled Electrical Control Apparatus.

A general object of the present invention is to provide a new andimproved electrical controller which will respond to minute changes in avariable and produce an electrical output signal which may be used tocontrol the variable. More specifically, the present invention isconcerned with a galvanometer positioned vane which changes anelectrical characteristic of an electrical circuit. The changes aredetected and amplified to produce an output control signal which isdependent upon the position of the vane.

In present day process control problems, it is frequently necessary toprovide controllers which will follow very small changes in the variableof the process so that corrective action can be taken to hold thevariable at its desired value. Such controllers may also require rateand resetting operation in order to hold the variable at its desiredposition. In designing such controllers, care must be taken to see thatthe operation of the controller does not affect the variable sensingunit except as it may change the variable, In addition, the controllermust accurately follow changes in the variable and produce an outputcontrol signal which will eliminate prolonged deviations of the variablefrom its desired value. In addition, such apparatus must have easilymade proportional band and centering adjustments.

It is accordingly a further object to provide a new and improvedelectrical controller which is characterized by its large response tominute input signals.

vAnother object of the present invention is to provide an electricalcontroller which will produce a direct current signal which will followan input signal of a variable and when amplified will be a controlsignal for maintaining the variable at a desired value.

Still another object is to provide an electrical controller having avariable positioned galvanometer which positions a vane in an electricalcircuit and the vane is not appreciably loaded by the electricalcircuit.

A still further object is to provide an electrical controller forproducing a direct current which varies in magnitude and polarity withvariations in a variable where the direct current signal is amplifiedwith rate and reset components added thereto.

Another object of the present invention is the provision of a directcurrent controller having an amplifier with internal resetting apparatusfor producing a varying output signal with a continued input errorsignal.

The various features of novelty which characterize the invention arepointed out with particularity in the claims annexed hereto and forminga part of this specification. For a better understanding of theinvention, however, its advantages, and specific objects obtained withits use, reference should be had to the accompanying drawings anddescriptive matter in which is illustrated and described a preferredembodiment of the invention.

The single figure of the drawing shows schematically one manner in whichthe preferred embodiment of the invention may be arranged.

Referring now to this single figure, the numeral represents a furnacewherein a variable, such as temperature, is to be maintained at adesired value. For detecting the magnitude of the variable there isprovided a thermocouple 11 which is connected to a suitable galvanometerassembly 12. This galvanometer 12 positions, a vane 13 relative to apair of coils 14 and 15 in the elec-- trical controller 16 which formsthe basic partof the present invention. The output of the controller 16is upon a pair of electrical leads 17 and 18 and the signal on theseleads will operate upon a controller 19 which will position a suitablevalve 20 which may regulate the flow of fuel through a conduit 21 to thefurnace 10. The flow of the fluid through the conduit 21 will beregulated so as to maintain the temperature within the furnace at adesired value. While the apparatus is shown controlling temperature, itis to be understood that any desired variable, such as flow, pressure,and the like may be controlled.

Referring more specifically to the controller 16, the source of energyfor the control signal is derived from an oscillator section 25.Included in this oscillator section is a three electrode electronicdevice 26 having an anode 27, a cathode 28, and a control electrode 29.COD: nected in the anode circuit of the device 26 is a condenser 30which is arranged to resonate with a coil 31 which is the primarywinding of a transformer 32, Coupled to the coil 31 is an input coil 33which has one end thereof connected to the control electrode 29.Connected to the other end of the coil 33 are a pair of parallelconnected R.C. circuits 34 and 35. The circuit 34 comprises a condenser36 connected in parallel with a resistor 37 while the network comprisesa condenser 38 connected in parallel with a resistor 39. This oscillator25 is characterized by its oscillating at a high frequency for shortintervals with a delay between operations so that there is in effect anumber of high frequency pulses appearing across the transformer 32.

An output winding 40 on the output of transformer 32 serves to couplethe output of the oscillator section 25 to the input of a variabledetector section 41. This input comprises a transformer 42 connected tothe winding 40 by a primary winding 43 and a secondary winding 44. Thesecondary winding 44 is arranged for connection to the ends of a pair ofcoils 45 and 46, the latter of which is comprised of the two coilsections 14 and 15 as set forth above. The coils 45 and 46 form a typeof voltage divider across the secondary 44 and, by reason of the outputtap 47, there is an apparent bridge type of network which may beunbalanced depending upon the relative magnitudes of the coils 45 and46.

Also included in the Variable detector section 41 are a pair ofassymmetrically conducting devices 48 and 49 which are shown in thedrawing as conventional rectifiers. Associated with the output of therectifier 48 isa resistor 50 while associated with the output of therecti fier 49 is a resistor 51. A condenser 52 cooperates with n theresistor 50 as a filter condenser as 53 relative to the resistor 51.

The output of this detector section will be in the form of a directcurrent signal whose polarity and magnitude does the condenser will bedirectly dependent upon the magnitude of the variable originating fromthe furnace 10.

Connected to the resistors 50 and 51 is the amplifier portion of" thepresent apparatus indicated by the numeral 55. The amplifier portionincludes a pair of control electrode controlled electronic devices 56and 57 which are differentially connected to the resistors 50 and 51.The electronic device 56 comprises an anode 58, a control electrode 59,and a cathode 60 while the device 57 Patented Aug. 29, 1961..

comprises an anode 61, a control electrode 62', and a cathode 63.

The input to the device 57 comprises a rate circuit in the form of aresistor 65 having a condenser 66 connected in parallel therewith. Alsoincluded is a further pair of resistors 67 and 68.

Associated with the input of the electronic device 57 a further ratenetwork comprising a resistor 69 having a condenser 70 connected inparallel therewith and a pair of resistors 71 and 72.

The output of the electronic device 56 comprises a resistor 73 while theoutput of the electronic device 57 includes a resistor 74. For supplyingenergy to both of the electronic devices there is provided a battery 75connected to the junction between the resistor 73 and 74 at one end andat the other end connected to a resistor 76. Connected between thecathodes of the devices 56 and 57 is a potentiometer 77' which acts tobalance the current flows through the two devices and a rheostat 78which may be used to adjust the gain of the amplifier to a high value.If the negative feedback circuits, not yet set out, are not used, therheostat 78 acts as a proportional band adjustment.

A pair of feedback cricuits are provided for each of the electronicdevices with negative feedback for the electronic device 56 beingprovided by a condenser 80 connected in series with an adjustableresistor 81 between the anode 58 and the control electrode 59. In theelectronic device 57, the negative feedback path is through a condenser82 connected in series with an adjustable resistor 83. This negativefeedback circuit is between the anode 61 and the control electrode 62.An additional pair of condensers 80A and 82A may be connected inparallel with the condensers 80 and 82 by suitable switches to vary thereset rate of the apparatus. Positive feedback is obtained in theamplifier section 55 by a connection from the anode 58 through aresistor 84 to the control electrode 62 as well as a connection from theanode 61 through a resistor 85 to the control electrode .59. This crossconnected positive feedback will be explained in the course of theexplanation of the operation of the apparatus.

Considering the operation of the present apparatus, attention shouldfirst be directed to the operation of the oscillator section 25.Electrical components of the networks 30 and 35 are selected so that theR.C. time constant of the network 34 is relatively long. At the time ofinitial adjustment, the network 35 will be shorted out and network 34tuned so as to give a desired stable level of operation. With the timeconstant of the network 35 selected to be relatively long, theoscillator will oscillate at a high freqnency in pulses of relativelyshort duration. At the start of each pulse, the oscillator goes rapidlyinto an intense oscillatory condition with the operation being class Cas far as the device 26 is concerned. The intensity is limited by theshort time constant network 34. With the class C operation, there willbe control electrode current flow which will tend to slowly change thecondenser 38. This slow change will cause a decrease in the oscillatoryintensity due to the negative biasing action of the change on thecondenser 38 until the section goes out of oscillation. This is shown inthe insert A on the drawings. Such an oscillator as this minimizes theside band frequencies which will be present in the detector section aswell as the loading effect on the vane 13, as will be hereinafterexplained.

Representative data on the oscillator section 25 is as follows:

20.5 mc. per second.

3 per second.

Oscillation frequency Pulsing rate... ..-;r..

The output of the oscillator is coupled to the detector 41 by thecoupling link 4043 and this coupling link is arranged so there will beno capacitive coupling into the transformer 42 from the oscillatorsection 25.

The pulses of energy from the oscillator section 25 are applied acrossthe winding 44 and the coils 45 and 46. Inasmuch as the vane 13 isarranged for positioning between the coil sections 14 and 15, should theoscillations be continuous, there is a tendency for the coils to loadand force the vane from its normal position against the operating forcesfrom the galvanometer coil. This is due to circulating currents beinginduced in the core which currents act in the field of the coils to movethe vane away from the coils. This loading of the vane may be sufficientto render ineffective the input control action of the galvanometer coiland thus render the apparatus effectively useless. By providing onlyshort pulses of energy, this loading of the vane by the coil sections 14and 15 is reduced to a minimum.

As the voltage drop across the coils 45 and 46 is dependent upon thefrequency applied, it is essential for stable operation that the sideband frequencies be at a minimum. Such is obtained from an oscillator ofthe present type. It was found that when network 34 was omitted theoutput of the bridge circuit 41 was smaller for a given unbalance andbalance point of the bridge was less sharp than when the network waspresent. It was believed that this was due to the sharpness of thepulses leading to a broad frequency spectrum being applied to the bridge41 and also an extremely low duty factor. This low duty factor, which isthe pulse length relative to the total cycle, is selected to be acompromise between minimum loading of the vane and maximum output fromthe section 41.

With the variable in the furnace 10 being at the desired value, andassuming that this value will produce a vane position wherein the vane13 is halfway between the coils 14 and 15, the impedances of the coils45 and 46 should be substantially the same so that the relative voltagedrops thereacross due to the input signal applied to their ends will besubstantially the same. The voltages appearing across the coils 45 willbe rectified by the rectifier 48 and there will appear upon the resistor50 a direct current voltage which is filtered by the action of thecondenser 52. The voltage across the coil 46 will be rectified by therectifier 49 and this will produce a direct current voltage across theresistor 51 which will be filtered by the. condenser 53. If there is abalanced condition, the voltage across the resistor 50 will be equal tothe voltage across the resistor 51. Under such circumstances, with thepolarities at the rectifier ends being the same, there will be zero netvoltage across the two resistors applied to the input of the amplifiersection 55.

Should the variable within the furnace 10 change so that the vane 13 ismoved out from between the coils 14 and 15 the inductance of the coil 46will increase and this increase will cause there to be a larger voltagedrop across the coil 46. This will appear across the output resistor 51as a larger direct current voltage so that the net voltage across thetwo resistors 50 and 51 will be such that the conductor will be positivewith respect to the conductor 91. Should the voltage within the furnace10 be reversed, the galvanometer will move the vane 13 between the coils14 and 15 so as to decrease the amount of inductance. This will meanthat there will be a decrease across the coil 46 and a resultantdecrease in voltage across the resistor 51. The net voltage on theconductors 90 and 91 will be such that the conductor 91 will now bepositive with respect to the conductor 90.

It will thus be seen that section 41 will produce a direct currentsignal whose polarity and magnitude in the output conductors 90 and 91will be dependent on the magnitude of the variable within the furnace10. This direct current signal will then be amplified by amplifiersection 55.

The input circuit leading to the devices 56 and 57 includes a ratenetwork which has the effect of producing a voltage proportional to therate of change of the direct current signal on the resistors 50 and 51.The input circuit for the electronic device 59 may be traced fromconductor 91 through the resistor 65, resistor 67, resistor 68 andconductor 92 back to the resistor 50. In the event that the condenser 66is not connected across the resistor 65, appearing across the resistor68 on the electronic device 56 will be that portion of the input signaldivided by the resistors 65, 67 and 68. However, with condenser 66connected across the resistor 65, this shorts out the resistor 65 duringchanges of the signal so that the signal is now divided across theresistors 67 and 68. In that arrangement, the condenser 66 whenconnected across the resistor 65 will introduce to the input aderivative action of the control signal appearing across the resistor50. After the input signal has stabilized, the input voltage across theresistor 65 will have stabilized to its normal value and the condenser66 will have been charged to that value. The operation of the resistor69 and the condenser 70 on the input of the electronic device S7 is thesame as that on the input of the electronic device 56.

The net signal on the control electrode 59 will be the voltage dropacross the resistor 68. This will mean that there will appear across theresistor 73 on the output of the device 56 an amplified volt-age. Thesame will be true across the resistor 74 in the output of the electronicdevice 57. The electron current flow through the device 56 may be tracedfrom the cathode 60, anode 58, conductor 93, resistor 73, battery 75,resistor 76, potentiometer 77, back to cathode 60.

The electron current flow circuit for the device 57 may be traced fromthe cathode 63 to the anode 61, conductor 94, resistor 74, battery 75,and resistor 76 through potentiometer slide wire 77 to the cathode 63.This will result in their appearing across the resistor 73, and 74, aswell as the output conductors 17 and 18, a direct current signal whichwill be proportional to the signal on resistors 50 and 51. With thecondensers 66 and 70 in the circuit, there will be superimposed thereona derivative signal which will tend to prevent hunting or overshootingof the variable in the furnace and will cause the variable to assume itsdesired value.

Consider now the operation of the feedback circuits in the amplifiersection 55. Positive feedback is obtained in the apparatus by aconnection from the anode 58 through the resistor 84 to the controlelectrode 62 as well as through the resistor 85 connected between theanode 61 and the control electrode 59. Thus, when the control electrode59 becomes more positive, the feedback through resistor 84 will becomenegative and this negative signal will be applied through the resistor84 to make the control electrode 62 more negative. With the controlelectrode 62 becoming negative, the anode 61 will become positive andthis positive potential will be applied through the resistor 85 to thecontrol electrode 59 to increase further the positive potential on thecontrol electrode. In the absence of some further feedback the amplifiersection would tend to have infinite gain, but with the actual gain beinglimited by the saturating characteristics of the electronic device 57.This runaway characteristic is prevented by the negative feedbacknetwork in electronic device 56 in the form of the condenser 80connected in series with the resistor 81. The initial effect of thenegative feedback circuit on the control electrode 59 is to produce avoltage counter the positive feedback voltage derived from anode 61.Thus, with a step input signal, the control electrode 59 will be awareonly of the difference between the positive feedback signal and thenegative feedback signal. Likewise, the negative feedback circuit forthe electronic device 57 is a condenser 82 connected in series with aresistor 83. As before, the negative feedback 6 action, on a step input,may be partially balanced by the positive feedback from the anode, sothat only thedifference appears on the control electrode 62.

In the event that the control variable should deviate from the desiredvalue continuously so that there is a continuous signal on theconductors 90 and 91, it is desired that a resetting action take placeso as to gradually eliminate this deviation.

This resetting or integrating action is obtained by the condenser slowlycharging and slowly removing a portion of the negative feedback to thecontrol electrode 59. The resetting action for the electronic device 57is obtained by the condenser 82 gradually charging to remove some of thenegative feedback of control electrode 62. The only way this circuit canmaintain a balance is for the amplifier devices to increase their outputvoltage so as to counteract the charging of the respective condensers.This slow increase in the maintaining of a stable condition on theinputs of the electronic devices 56 and 57 produces a control signal onthe conductors 17 and 18 which will be gradually increasing. Thisgradual increase will cause the controller 19 to regulate the valve 20gradually changing the flow of fuel to the furnace 10 to remove theunbalanced condition in the furnace. Due to the long time constants ofthe discharging circuits for the condensers 80 and 82, the change levelwill tend to hold over a period of time and there is thus obtained areset action which has the effect of eliminating any deviations in thefurnace 10. With the present arrangement, the apparatus is arranged tohave maximum gain with accompanying stability even with rate and resetsuperimposed upon the basic control signal. While the apparatus can beoperated satisfactorily with only one side including rate and resettingcomponents, the operation is greatly enhanced by the presence of thedouble rate and reset circuit configuration.

To change the proportional band of the apparatus, the adjustableresistors 81 and 83 may be adjusted with the adjustment having theeffect of changing the feedback to the electronic devices 56 and 57. Toeffect a balance between the current flows in the devices 56 and 57,there is provided the potentiometer 77 which may be adjusted to give-adesired balanced output when the input from the detector section 41indicates a balance, or with no input to the amplifier section 55.

While in accordance with the provisions of the statutes, there has beenillustrated and described the best forms of the invention known to me,it will be apparent to those skilled in the art that changes may be madein the form of the apparatus without departing from the spirit of theinvention as set forth in the appended claims, and that in some casescertain features of the invention may be used to advantage without theuse of other corresponding features.

What is claimed is:

1. In an electrical controller for producing an output signalproportional to the positioning of an element in an electrical circuit,the combination comprising, an electrical oscillator section forproducing a train of high frequency pulses, said section comprising anelectronic device having an anode, cathode, and control electrode, atuned tank circuit connected to said anode, a coupling coil coupled tosaid tank circuit connected between said control electrode and saidcathode, and a pair of R.C. circuits serially connected in said lastnamed connection, said R.C. circuits being arranged to cause saidoscillator to cyclically produce short high frequency pulses.

2. An oscillator for an electrical controller comprising, an electronicdevice having an anode, cathode, and control electrode, a tuned resonanthigh frequency tank circuit connected to said anode, a coil inductivelycoupled to said tank circuit and connected between said controlelectrode and said cathode, and a pair of R.C. circuits serially 7 8cdnnect'ed in said lastnamed connection, one of said pair ReferencesCited in the file of this patent l hving a relatively short timeconstant and the other UNITED STATES T N 1 having a relatively long timeconstant so that said oscil- 2,426,021 Hausz t a1 fi- 5 lator willcyclically operate for short periods at a relar 2,437,970 Reich ag; 5191 ti y s e y in en i y. 2,544,741 Varela Mai: 13, 1951

